A wire grid polarizer (WGP) can be used to divide light into two different polarization states. A high percent of one polarization state can pass through the WGP and a high percent of the other can be absorbed or reflected. The effectiveness or performance of a WGP is based on a very high percent transmission of one polarization (Tp) and minimal transmission of an opposite polarization (Ts). It can be beneficial to have high contrast (Tp/Ts). The percent reflection of the opposite polarization (Rs) can also be an important indicator of polarizer performance.
Wires of WGPs, especially for polarization of visible or ultraviolet light, can have small, delicate wires with nanometer-sized pitch, wire-width, and wire-height. WGPs are used in systems (e.g. computer projectors, semiconductor inspection tools, etc.) that require high performance. Small defects in the WGP, such as corroded wires and collapsed wires can significantly degrade system performance (e.g. distorted image from a computer projector). Ordinary handling can cause the wires to collapse. Therefore, it can be important to protect the wires from corrosion and mechanical damage.
Oxidation can degrade performance by adversely affecting contrast and/or Rs. As an aluminum wire forms a natural oxide over time, the underlying, substantially-pure aluminum is consumed, thus reducing the size of the substantially-pure aluminum wire and changing polarization characteristics of the WGP.